Bug 846144 - Don't optimize backgrounds to an ImageLayer if they have border-radius clipping. r=roc,a=akeybl

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extra : rebase_source : 42985b65cd86d227149dcfc6d106952cf67e2b1d
Bug 815591. Don't build nsDisplayBackgroundColor if there is no background color and we're not going to do hit-testing. r=mattwoodrow,a=akeybl

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extra : rebase_source : c953ca7a94b562ac20c98c0845ec28512d8df3ac